Refactor build script

gulpfile.babel.js

@@ -1,10 +1,10 @@
-const gulp  = require('gulp')
+import gulp from 'gulp'
-const fs    = require('fs')
+import fs from 'fs'
-const path  = require('path')
+import path from 'path'
-const merge = require('event-stream').merge
+import {merge} from 'event-stream'
-const map   = require('map-stream')
+import map from 'map-stream'
-const spawn = require('child_process').spawn
+import {spawn} from 'child_process'
-const $     = require('gulp-load-plugins')()
+const $ = require('gulp-load-plugins')()
 
 // Tasks
 gulp.task('clean', () => {

package.json

@@ -26,6 +26,7 @@
     "crx": "^0.4.4",
     "event-stream": "*",
     "firefox-profile": "~0.3.6",
+    "gulp": "^3.9.0",
     "gulp-autoprefixer": "0.0.8",
     "gulp-babel": "^6.1.0",
     "gulp-clean": "^0.3.1",